Vapor/Charcoal Cannister

I didn't read the jeep article (figuring this was going on an A-body)
but the acdelco one I INTENDED to mention (215-153, not 215-513) has three ports
one for the tank
one for the carb vent
and a purge line

unless the jeep has a vacuum activated purge valve build in, I don't see why you would need a fourth one?